President Vladimir Putin says Russia will conduct a military operation in eastern Ukraine.
In a televised address early on Thursday morning, Mr Putin said the action comes in response to threats coming from Ukraine.
He added that Russia does not have a goal to occupy Ukraine, but said the responsibility for bloodshed lies with the Ukrainian “regime”.
Mr Putin also warned other countries that any attempt to interfere with the Russian action would lead to “consequences they have never seen”.
He accused the US and its allies of ignoring Russia’s demand to prevent Ukraine from joining Nato and offer Moscow security guarantees.
He said the Russian military operation aims to ensure a “demilitarisation” of Ukraine, adding that all Ukrainian servicemen who lay down arms will be able to safely leave the zone of combat.
The announcement came just after airspace over all of Ukraine was shut down to civilian air traffic, and at the same time as an emergency meeting of the UN Security Council was taking place.
On Wednesday night, Ukrainian President Volodymyr Zelensky made an emotional televised address in Russian following the approval of a 30-day state-of-emergency order handed the government sweeping powers in the interest of national security.
“The people of Ukraine and the government of Ukraine want peace. But if we come under attack that threatens our freedom and lives of our people we will fight back,” he said, as he rejected Moscow’s claim Ukraine is a threat to Russia.